JP2013143187A - Solid oxide fuel battery, and material for forming cathode of solid oxide fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for forming a cathode of a solid oxide fuel battery which has good electrode performance as an electrode, and which is arranged to reduce the thermal expansion and reduction expansion.SOLUTION: The present invention provides a material for forming a cathode of a solid oxide fuel battery 50. The material is in a composite condition, and comprises: a perovskite type oxide expressed by the general formula, (LaSr)(CoFe)O(where x is a real number satisfying the condition, 0.1≤x≤0.5; y is a real number satisfying the condition, 0.1≤y≤0.5; and δ is a value determined so as to satisfy a charge neutral condition); and a perovskite type oxide expressed by a general formula, (LaSr)(TiFe)O(where x is a real number satisfying the condition, 0.1≤x≤0.5; y is a real number satisfying the condition, 0.1≤y≤0.5; and δ is a value determined so as to satisfy the charge neutral condition).

Description

  The present invention relates to a material used for forming a cathode (air electrode) of a solid oxide fuel cell, and a solid oxide fuel cell constructed using the material.

A solid oxide fuel cell (SOFC: hereinafter referred to simply as “SOFC”) has high power generation efficiency and can use various fuels among various types of fuel cells. It is being developed as a next-generation power generator with less environmental impact.
A typical SOFC structure (single cell) has a porous structure on one side of a dense solid electrolyte (eg, a dense membrane layer) made of an oxygen ion conductor (typically an oxygen ion conductive ceramic body). A cathode (air electrode) is formed, and a porous anode (fuel electrode) is formed (for example, laminated) on the other surface. A fuel gas (typically H ₂ (hydrogen)) is formed on the surface of the solid electrolyte on the side where the fuel electrode is formed, and O ₂ (oxygen) is formed on the surface of the solid electrolyte on the side where the air electrode is formed. Each of the contained gases (typically air) is supplied.

As a cathode material of SOFC, a perovskite type oxide as shown by a general formula (LnAe) MO ₃ (where Ln = La, Ae = Sr, M = Mn, Fe, Co, etc.) is often used. It has been.
Patent documents 1 and 2 are mentioned as conventional technology about this oxide. For example, Patent Literature 1 exemplifies an oxygen separation membrane in which a part of the M element in the above general formula is replaced with titanium (Ti) and aluminum (Al). Patent Document 2 exemplifies an oxygen separation membrane in which a part of the M element is substituted with zirconium (Zr).

JP 2007-51035 A JP 2007-51036 A

By the way, in recent years, research for lowering the operating temperature of SOFC has been promoted from the viewpoint of cost reduction and application expansion of SOFC. Therefore, a material represented by the general formula (LaSr) (CoFe) O ₃ (hereinafter referred to as “LSCF”) has attracted attention as a cathode material for a medium-low temperature (for example, 600 ° C. to 800 ° C.) operation type SOFC. The LSCF is a so-called oxygen ion-electron mixed conductor, and can exhibit high electrode catalyst ability even in a relatively low temperature region.
However, since the LSCF has a larger thermal expansion than other cathode materials, the thermal shock (for example, the temperature at the time of non-use (typically normal temperature) and the temperature range at the time of use (for example, 600 ° C. to 800 ° C.) There is a problem that durability against repeated heating and lowering is low. In addition, since the reductive expansion is large, there is a possibility that defects such as cracks may occur when the fuel gas leaks and enters the cathode. Therefore, when LSCF is used as a cathode material, a material represented by a general formula: CeGdO ₂ (hereinafter referred to as “GDC”) in which ceria (CeO ₂ ) is doped with gadolinia (Gd ₂ O ₃ ). Mixing and using these is also under consideration. However, the GDC is very expensive and is not preferable from the viewpoint of cost reduction. Furthermore, since the LSCF is highly reactive with a zirconia-based oxide generally used as a solid electrolyte, when the LSCF is used as a cathode, a reaction inhibiting layer (both intermediate layer and protective layer) is formed between the LSCF and the solid electrolyte. Need to be formed).

  The present invention has been made in view of such problems, and an object of the present invention is to provide an SOFC cathode material that has excellent performance as an electrode and has reduced thermal expansion and reduction expansion. is there. Moreover, this invention provides the SOFC which comprised the cathode using the said material as another side surface.

In order to achieve the above object, the present invention, the general formula _{(La 1-x Sr x)} (Co y Fe 1-y) O 3-δ ( here, x satisfies 0.1 ≦ x ≦ 0.5 Real Y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined so as to satisfy the charge neutrality condition.) (Hereinafter referred to as “LSCF”) that a.) the general formula _{(La 1-x Sr x)} (Ti y Fe 1-y) O 3-δ ( here, x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is 0 ..Ltoreq.y.ltoreq.0.5, and .delta. Is a value determined so as to satisfy the charge neutrality condition.) Perovskite oxide (hereinafter referred to as "LSTF"). A material for forming a cathode of a solid oxide fuel cell comprising a composite state including both is provided. The
The material in the composite state can exhibit excellent performance as an electrode even in a relatively low temperature range (for example, 600 ° C. to 800 ° C.). In addition, since thermal expansion and reductive expansion are kept relatively small, there is little expansion and contraction with respect to temperature changes and the like, and the durability of SOFC can be improved by using such materials. Furthermore, since LSCF and LSTF have low reactivity, SOFCs equipped with electrodes composed of a composite state of LSCF and LSTF can be used stably for a long period of time. For this reason, the material disclosed here can be used suitably as a cathode material of SOFC.

In a preferable embodiment of the material disclosed herein, a mass ratio of the LSCF to the LSTF is 80:20 to 30:70.
A material made of a composite state that satisfies the above-described mass ratio has excellent performance as an electrode, and thermal expansion and reductive expansion are further suppressed. For this reason, the effect of this invention can be exhibited further and it can use suitably as a cathode material of SOFC.

Further, in a preferable embodiment of the material disclosed herein, it is mentioned that the material contains at least one dispersion solvent and is prepared in a slurry form (including a paste form and an ink form).
The materials disclosed herein are used to form SOFC cathodes. In such an application, in order to stably produce a homogeneous cathode layer, it is possible to preferably use a material prepared by dispersing (or dissolving) the constituent material of the cathode in one or more kinds of dispersion solvents to prepare a slurry.

According to the present invention, there is also provided a solid oxide fuel cell comprising an anode, a solid electrolyte, and a cathode, wherein the cathode has the general formula (La _1-x Sr _x ) (Co _y Fe _1-y ) O _{3− δ} (where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. And a perovskite oxide (LSCF) represented by the general formula (La _1-x Sr _x ) (Ti _y Fe _1-y ) O _3-δ (where x is 0.1 ≦ x ≦ A real number satisfying 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition.) (LSTF) and a solid oxide fuel cell (SOF) C) is provided.
The SOFC provided with the cathode can exhibit high power generation performance. Moreover, since thermal expansion and reductive expansion are kept relatively small, it has excellent durability and can be used stably for a long period of time.

In a preferred aspect of the SOFC disclosed herein, a mass ratio of the LSCF and the LSTF in the cathode is 80:20 to 30:70.
The cathode has excellent performance as an electrode, and thermal expansion and reductive expansion are further suppressed. Therefore, in the SOFC using such a cathode, higher power generation performance (for example, the maximum power density at an operating temperature of 700 ° C. is 0.1 W / cm ² or more) and durability can be achieved at a higher level.

In a preferred aspect of the SOFC disclosed herein, the cathode, the solid electrolyte, and the anode are laminated in layers, and the thickness of the cathode in the laminated structure is 10 μm or more and 100 μm or less.
In the cathode, since thermal expansion and reductive expansion are suppressed, even when the thickness of the electrode is relatively large, a problem (for example, generation of cracks) due to a temperature change or the like hardly occurs. For this reason, in the SOFC using such a cathode, it is possible to stably exhibit excellent power generation performance over a long period of time.

In a preferred aspect of the SOFC disclosed herein, the cathode having the laminated structure is formed directly without providing a reaction inhibiting layer on the solid electrolyte.
As described above, when LSCF is used as the cathode material, a reaction inhibiting layer is generally formed between the solid electrolyte and the cathode due to the problem of reactivity with the solid electrolyte (typically zirconia oxide). There is a need to. However, since the cathode disclosed here can be formed directly on the solid electrolyte, it is simple and can reduce battery resistance. For this reason, the SOFC using such a cathode is excellent in productivity and can exhibit excellent power generation performance.

Furthermore, the present invention provides a method for producing a solid oxide fuel cell comprising an anode, a solid electrolyte, and a cathode. In the manufacturing method provided herein, an anode-solid electrolyte laminate comprising the anode and a solid electrolyte formed on the anode is prepared, and the surface on the solid electrolyte side of the laminate is disclosed herein. By applying any one of the cathode materials (typically, a material comprising a composite state containing both LSCF and LSTF described above) and firing the laminate to which the materials are applied. Forming.
In the manufacturing method disclosed here, the difference in thermal expansion coefficient (thermal expansion coefficient) between the cathode and other constituent materials (for example, members constituting the solid electrolyte and the power generation system) is suppressed to be small. Inconveniences (for example, generation of cracks) due to Further, since the reactivity between the cathode material and the solid electrolyte is low, there is no need to provide a reaction inhibiting layer on the solid electrolyte. For this reason, it is possible to more easily manufacture an SOFC having excellent durability while having high power generation performance.

In a preferred embodiment of the production method disclosed herein, the material is applied such that the thickness of the cathode formed by the firing is not less than 10 μm and not more than 100 μm.
In the manufacturing method disclosed here, since thermal expansion and reductive expansion of the cathode are suppressed, even when the cathode layer is relatively thick, it has excellent durability. For this reason, an SOFC using such a cathode can exhibit stable power generation performance over a long period of time.

It is sectional drawing which shows typically the electric power generation system provided with SOFC based on one Embodiment of this invention. It is a figure which shows typically the manufacturing process of SOFC based on one Embodiment of this invention. It is a scanning electron micrograph of the surface of a cathode electrode (mass ratio of LSCF and LSTF is 100: 0) provided in the SOFC, according to a comparative example. It is a scanning electron micrograph of the surface of the cathode electrode (mass ratio of LSCF and LSTF is 70:30) provided in the SOFC according to one embodiment of the present invention. It is a scanning electron micrograph of the surface of the cathode electrode (mass ratio of LSCF and LSTF is 50:50) provided in the SOFC according to one embodiment of the present invention. It is a scanning electron micrograph of the surface of a cathode electrode (mass ratio of LSCF and LSTF is 0: 100) provided in the SOFC, according to a comparative example.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than the matters specifically mentioned in the present specification (for example, the configuration and manufacturing method of the power generation system) and the matters necessary for the implementation of the present invention are those of ordinary skill in the art based on the prior art in this field. It can be grasped as a design matter. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The material disclosed herein is characterized by comprising a composite state containing both LSCF and LSTF (hereinafter, a material containing both LSCF and LSTF may be simply referred to as “composite material”). Therefore, the content, composition, and the like of other components can be determined in light of various standards without departing from the object of the present invention.
Whether or not such an aspect is in a composite state is determined by, for example, a general scanning electron microscope (SEM) -energy dispersive X-ray spectroscopy (EDX). Can be confirmed by. More specifically, by analyzing (mapping) an image obtained by SEM observation using EDX, the element distribution state can be examined and judged.

According to the present invention, there is provided a solid oxide fuel cell including an anode, a solid electrolyte, and a cathode, wherein the cathode is formed in a state where LSCF and LSTF are mixed. SOFC). A SOFC equipped with the cathode can exhibit high power generation performance. Moreover, since thermal expansion and reductive expansion are kept relatively small, it has excellent durability and can be used stably for a long period of time.
The cathode using the composite material disclosed herein is an SOFC having various structures, for example, a conventionally known sheet shape (Planar), a tube shape (Tubular), or a flat tube shape in which a peripheral side surface of a cylinder is vertically crushed. It can be suitably used for SOFC such as (Flat tubular), and is not particularly limited in shape or size.

An example will be described with reference to FIG. FIG. 1 is a diagram schematically illustrating a cross-sectional configuration of a power generation system including the SOFC 50 disclosed herein. The SOFC 50 having the structure shown here is an anode-supported SOFC, and is formed on a sheet-like anode (fuel electrode) 10 serving as a support (base material) and at least a part of the surface of the anode 10 (membrane). A solid electrolyte 20 and a sheet-like cathode (air electrode) 30 formed on the surface of the solid electrolyte 20 are laminated. Then, the end 12 of the anode 10 and the joining surface of the gas pipe 60 that supplies the fuel gas (typically H ₂ (hydrogen)) are joined by the connecting member 40, and the gas (fuel gas or air) flows out. And / or sealed from inflow. The cathode 30 has a structure exposed to the outside air. When a current is applied to such a power generation system, oxygen in the oxygen-containing gas (air) becomes oxide ions (oxygen is ionized) at the cathode 30. The oxide ions reach the anode 10 from the cathode 30 through the solid electrolyte 20 and are supplied to the anode 10. Then, electricity is generated by reacting with hydrogen (H ₂ ) in the fuel gas and releasing electrons.

  The anode (fuel electrode) 10 constituting the SOFC 50 disclosed herein has a porous structure. Note that the shape of the anode only needs to be configured so as to be in contact with the fuel gas supplied to the SOFC, and can be appropriately selected according to the shape of the SOFC described above. In the SOFC 50 having the configuration shown in FIG. 1, a sheet-like anode 10 formed relatively thick is formed as a support for the SOFC 50. The thickness of the anode 10 as the support is typically about 0.1 mm to 10 mm, and preferably about 0.5 mm to 5 mm, but is not limited to this thickness.

  Examples of the material constituting the anode include nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru) and other platinum group elements, and cobalt (Co). , Lanthanum (La), strontium (Sr), titanium (Ti) and the like, and / or metal oxides composed of one or more metal elements. Specific examples include metals and metal oxides composed of platinum group elements such as Ni, Co, and Ru. Of these, Ni is a particularly preferred metal species because it is cheaper than other metals and has a sufficiently high reactivity with fuel gas such as hydrogen. Moreover, the composite which mixed these metals and metal oxides can also be used. For example, a composite of the anode constituent material (metal or metal oxide) and a solid electrolyte constituent material described later can be used. More specifically, for example, nickel (Ni) or ruthenium (Ru), stabilized zirconia (for example, yttria stabilized zirconia (YSZ), calcia stabilized zirconia (CSZ), scandia stabilized zirconia (ScSZ), etc.) The cermet is a preferred example. Although not particularly limited, for example, the mixing ratio (mass ratio) of the anode constituent material and the solid electrolyte constituent material described later is about 90:10 to 40:60 (more preferably, about 80:20 to 45: 55).

  The solid electrolyte 20 constituting the SOFC 50 disclosed herein has a dense structure. The solid electrolyte 20 is laminated on the anode 10, and the shape can be appropriately changed according to the shape of the anode 10. The film thickness of the solid electrolyte 20 is typically about 5 μm to 100 μm, preferably about 10 μm to 30 μm, but is not limited to such a film thickness.

As a material constituting such a solid electrolyte, a compound having high oxide ion conductivity is preferably used. For example, zirconium (Zr), cerium (Ce), magnesium (Mg), scandium (Sc), titanium (Ti), aluminum (Al), yttrium (Y), calcium (Ca), gadolinium (Gd), samarium (Sm) ), Barium (Ba), lanthanum (La), strontium (Sr), gallium (Ga), bismuth (Bi), niobium (Nb), tungsten (W), and the like. It is preferable. More specifically, a stabilizer (for example, yttria (Y ₂ O ₃ ), calcia (CaO), scandia (Sc ₂ O ₃ ), magnesia (MgO), ytterbia (Yb ₂ O ₃ ), erbia (Er ₂ Zirconia (ZrO ₂ ) whose crystal structure has been stabilized with O ₃ )) or a dopant (for example, yttria (Y ₂ O ₃ ), gadolinia (Gd ₂ O ₃ ), samaria (Sm ₂ O ₃ ), etc.) Doped ceria (CeO ₂ ) is a preferred example. In particular, yttria-stabilized zirconia (YSZ) in which an oxide of yttrium (Y) (for example, yttria (Y ₂ O ₃ )) is dissolved, or an oxide of scandium (Sc) (for example, scandia (Sc ₂ O ₃ )). Scandia-stabilized zirconia (ScSZ) or the like in which a solid solution is dissolved can be particularly preferably used.

  The cathode (air electrode) 30 constituting the SOFC disclosed here has a porous structure like the anode 10. The cathode 30 is laminated on the solid electrolyte 20, and the shape can be appropriately changed according to the shape of the solid electrolyte 20. The thickness of the cathode 30 is typically about 1 μm to 200 μm, preferably about 5 μm to 100 μm, more preferably 10 μm to 100 μm, but is not limited to such thickness. Since the cathode made of the material disclosed herein is suppressed from thermal expansion and reductive expansion, even when the electrode thickness is relatively large, problems (for example, generation of cracks) due to temperature changes are unlikely to occur.

As a material constituting such a cathode, the general formula _{(La 1-x Sr x)} (Co y Fe 1-y) O 3-δ ( here, x is a real number satisfying 0.1 ≦ x ≦ 0.5 , Y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined so as to satisfy the charge neutrality condition.) And a perovskite-type oxide (LSCF) represented by the general formula ( La _1-x Sr _x ) (Ti _y Fe _1-y ) O _3-δ (where x is a real number satisfying 0.1 ≦ x ≦ 0.5, and y is 0.1 ≦ y ≦ 0.5) And a composite state (composite material) including both perovskite type oxides (LSTFs) represented by (5).

The value of “x” in the above general formula is a value indicating the ratio of “La element” to “Sr element” in the perovskite oxide. The possible range of “x” is a range of 0.1 ≦ x ≦ 0.5 (preferably 0.1 ≦ x ≦ 0.4) as long as the structure can be maintained without destroying the perovskite structure. Any real number can be used as long as it is within.
The value of “y” in the above general formula is a value that determines the composition ratio between “Fe element” and “Co element (in the case of LSCF) or Ti element (in the case of LSTF)” in the perovskite oxide. . The value that “y” can take may be any real number as long as it is within the range of 0.1 ≦ y ≦ 0.5.
In the above general formula, the number of oxygen atoms may be 3 or less (typically less than 3). However, the number of oxygen atoms is the type and substitution ratio of atoms that substitute part of the perovskite structure (for example, “Sr element”, “(LSCF) Co element or (LSTF) Ti element)” in the formula) And other conditions, so as to satisfy the charge neutrality condition in the above general formula. Here, “δ”, which is a variable for determining the number of oxygen atoms in the above general formula, is typically a positive number not exceeding 1 (0 ≦ δ <1). As described above, the number of oxygen atoms in the above general formula varies depending on the other elements constituting the perovskite oxide, so that it is difficult to display accurately, and δ is omitted for convenience. May be described. That is, (3-δ) in the above general formula is not intended to limit the technical scope of the present invention.

The LSCF is a so-called oxygen ion-electron mixed conductor and has high performance as an electrode as compared with other perovskite oxides. Therefore, excellent performance can be exhibited even in a relatively low temperature range (for example, 600 ° C. to 800 ° C.). However, since the LSCF has a large coefficient of thermal expansion and reductive expansion, when used as it is as an SOFC electrode as shown in an example (Example 1) to be described later, the environmental change of the electrode (typically, the atmosphere (Such as cracks) due to changes in temperature and temperature). In such a case, an increase in resistance of the electrode, a gas leak, and the like occur, so that there is a possibility that the power generation performance is lowered or the power generation itself is not performed. On the other hand, the LSTF is characterized by low thermal expansion and reductive expansion, although the performance (power generation performance) as a battery is inferior to that of LSCF.
For this reason, the composite material which consists of a composite state of LSCF and LSTF disclosed here can exhibit the outstanding performance as an electrode also in a comparatively low temperature range (for example, 600 to 800 degreeC). In addition, since thermal expansion and reductive expansion are kept relatively small, there is little expansion and contraction with respect to temperature changes and the like, and the durability of SOFC can be improved by using such materials. Furthermore, since LSCF and LSTF have low reactivity, SOFCs equipped with electrodes composed of a composite state of LSCF and LSTF can be used stably for a long period of time. For this reason, the material disclosed here can be used suitably as a cathode material of SOFC.

In a preferred embodiment of the SOFC disclosed herein, the mass ratio of LSCF to LSTF in the cathode is 80:20 to 30:70. The cathode satisfying the above mass ratio has suppressed thermal expansion and reductive expansion, and can exhibit more excellent performance as an electrode. Therefore, SOFC using such a cathode can exhibit higher power generation performance (for example, power density at an operating temperature of 700 ° C. is 0.1 W / cm ² or more).

The composite material disclosed here may be made from a raw material, for example, or purchased. There is no particular limitation on a manufacturing method, and a method similar to a conventional method can be used. For example, first, compounds (LSCF and LSTF) as starting materials and other additives as required are added to a mixer such as a dry or wet ball mill at a predetermined blending ratio and mixed to prepare a mixed powder. The material used in this case is preferably one having an average particle size of 0.1 μm to 10 μm (preferably 0.3 μm to 3 μm, more preferably 1 ± 0.5 μm).
Next, the obtained mixed powder is annealed under suitable high temperature conditions. The annealing temperature may be set to 700 ° C. to 900 ° C. (preferably 800 ± 50 ° C.), and the time may be set to 30 minutes to 4 hours (preferably 30 minutes to 2 hours).
Then, the mixture after the annealing treatment is pulverized, and appropriately subjected to sieving and classification, for example, an average particle size of 0.1 μm to 10 μm (typically 0.1 μm to 3 μm, preferably 0.5 μm). A composite material (powder) of ˜2 μm, more preferably 0.5 μm to 1.5 μm is obtained. For the pulverization treatment, one or more of the conventionally used apparatuses can be used without any particular limitation. For example, a non-media type dispersing machine such as a jet mill or a planetary mixer, or a medium type dispersing machine such as a ball mill can be used. The conditions for the pulverization treatment (for example, pulverization speed and pulverization time) may be adjusted as appropriate so that a desired particle size can be obtained.
In the present specification, the “average particle diameter” means, for example, a particle diameter D ₅₀ (corresponding to a cumulative 50% in a volume-based particle size distribution measured by a particle size distribution measurement based on a conventionally known laser diffraction / light scattering method. Also called median diameter).

  As a preferred embodiment of the SOFC disclosed herein, the cathode 30 having the laminated structure is formed directly on the solid electrolyte 20 without providing a reaction inhibiting layer. As described above, when LSCF is used as the cathode material, a reaction inhibiting layer is generally formed between the solid electrolyte and the cathode due to the problem of reactivity with the solid electrolyte (typically zirconia oxide). There is a need to. However, since the cathode disclosed here can be formed directly on the solid electrolyte, it is simple and can reduce battery resistance. For this reason, the SOFC using such a cathode is excellent in productivity and can exhibit excellent power generation performance.

The form of the composite material disclosed herein may be, for example, the above-described powder form or a slurry form (including paste form and ink form) containing the powder and an arbitrary dispersion solvent. The slurry may be a solid (dried (or calcined)).
As the dispersion solvent, one or two or more of those capable of suitably dispersing the constituent materials of the composite material can be used without any particular limitation. As the solvent, either an organic solvent or an inorganic solvent may be used. Examples of the organic dispersion solvent include ether solvents, ester solvents, ketone solvents, and other organic solvents. In particular, terpineol, butyl diglycol acetate, isobutyl alcohol and the like are preferably used. In addition, the inorganic solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. Although the content rate of the solvent in a paste is not specifically limited, About 5-35 mass% of the whole slurry is preferable.

  If necessary, the slurry-like composite material disclosed herein may be added with a binder or other components that can be optionally added (for example, additives such as a thickener and a dispersant). In addition, the binder, additive, etc. which are used for a paste are not specifically limited, In paste manufacture, it can select from a conventionally well-known thing suitably and can be used. Examples of such a binder include cellulose or a derivative thereof. More specifically, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxyethylmethylcellulose, cellulose, ethylcellulose, methylcellulose, ethylhydroxyethylcellulose, butyral and salts thereof can be mentioned. Although the content rate of a binder is not specifically limited, It is preferable that it is contained in 2-20 mass% of the whole slurry.

As a composite material disclosed here, the thermal expansion coefficient (typically 12 × 10 ⁻⁶ / K ^{−1 to} 13 × 10 ⁶ ) of another constituent material (for example, a member constituting a solid electrolyte or a power generation system). Having a thermal expansion coefficient close to ⁻⁶ / K ⁻¹ ) is preferable, typically 16 × 10 ⁻⁶ / K ^{−1 to} 13 × 10 ⁻⁶ / K ⁻¹ , for example, 15 × 10 ⁻⁶ / K ^{−1 to} 14 × 10 ⁻⁶ / K ⁻¹ , preferably 15 × 10 ⁻⁶ / K ^{−1 to} 14.5 × 10 ⁻⁶ / K ⁻¹ . A cathode satisfying the above thermal expansion coefficient can change in temperature even if it is repeatedly raised and lowered between the operating temperature range (for example, 600 ° C. to 800 ° C.) and the temperature when not in use (typically normal temperature). The accompanying defects (for example, generation of cracks) are difficult to occur. For this reason, an SOFC using such a cathode can exhibit stable power generation performance over a long period of time.
In addition, the said thermal expansion coefficient is the temperature range of room temperature (25 degreeC)-500 degreeC or more (for example, 500 degreeC or 1000 degreeC), for example with the thermomechanical analyzer (TMA; Thermo Mechanical Analysis) using a differential expansion system. The arithmetic average value of the values measured at can be adopted. Specific conditions will be described in Examples described later.

Moreover, as a composite material disclosed here, it is preferable that the reduction expansion coefficient (%) is suppressed. Such a value is typically less than 1.0, preferably 0.8 or less, more preferably 0.7 or less. The reductive expansion coefficient is an index that quantitatively indicates a measure of the reduction durability (reduction expansion coefficient, that is, the thermal expansion coefficient in the reducing atmosphere) by dimensional change when heated in a reducing atmosphere. In the cathode satisfying the above reductive expansion rate, for example, when the fuel gas leaks and enters the cathode side, the reductive expansion is suppressed (that is, the durability under a reducing atmosphere is high). Is unlikely to occur. Therefore, the SOFC using such a cathode can exhibit stable power generation performance over a long period of time. Further, in this specification, “reduction expansion rate (%)” is the following formula when the thermal expansion coefficient in a reducing atmosphere is E _red (%) and the thermal expansion coefficient in an air atmosphere is E _air (%). Indicates the value given by (3).
[{(1 + E _red / 100) − (1 + E _air / 100)} / (1 + E _air / 100)] × 100 (3)

  Moreover, the method of manufacturing suitably the SOFC mentioned above is provided. The manufacturing method disclosed herein is a method for manufacturing a solid oxide fuel cell having a laminated structure including a porous anode, a solid electrolyte made of an oxide ion conductor, and a porous cathode. It is.

  Such a manufacturing method includes preparing an anode-solid electrolyte laminate composed of the anode and a solid electrolyte formed on the anode, and disclosing any one disclosed herein on the surface of the laminate on the solid electrolyte side. The cathode material (typically, the composite material described above) is applied, and the laminated body to which the material is applied is fired to form the cathode. In the manufacturing method disclosed here, the difference in thermal expansion coefficient (thermal expansion coefficient) between the cathode and other constituent materials (for example, members constituting the solid electrolyte and the power generation system) is suppressed to be small. Inconveniences (for example, generation of cracks) due to Further, since the reactivity between the cathode material and the electrolyte is low, there is no need to provide a reaction inhibiting layer. For this reason, according to the manufacturing method disclosed here, it is possible to more easily manufacture an SOFC that can exhibit high power generation performance while having high durability. A specific manufacturing method will be described in detail with reference to FIG.

<Preparation of anode-solid electrolyte laminate>
Here, the “anode-solid electrolyte laminate” indicates a state where the anode and the solid electrolyte are laminated, and there is no particular limitation on the method for preparing the anode-solid electrolyte laminate. Therefore, it is possible to use “anode manufacturing method” and “solid electrolyte manufacturing method” in the conventionally known SOFC manufacturing methods.
For example, as shown in FIG. 2A, first, an anode 10 having a porous structure is formed as a support substrate (support). Here, a cermet material is prepared by mixing a group 8-10 metal element material (for example, nickel material) and a stabilized zirconia (for example, YSZ). Next, the cermet material is dispersed in a solvent (for example, xylene) together with a binder (for example, a methacrylic ester polymer) and a dispersant (for example, sorbitan trioleate) to prepare a slurry anode material. Then, the anode material is formed by an appropriate forming method (for example, sheet forming), and the formed body is fired to form the sheet-like anode 10. It is good to perform the baking process of the said molded object by heating at the temperature of 1200 to 1400 degreeC for 1 hour-5 hours. In addition, you may perform the baking process of the material for anodes simultaneously with the baking process of the material for solid electrolytes mentioned later.

  Then, as shown in FIG. 2B, a solid electrolyte 20 is formed on the anode 10. Here, the raw material (for example, YSZ) of the above-described solid electrolyte 20 is dispersed in a solvent (for example, xylene) together with a binder (for example, methacrylic ester-based polymer) and a dispersant (for example, sorbitan trioleate), and used for a slurry-like solid electrolyte. Prepare the material. Next, the prepared solid electrolyte material is applied onto the anode 10 (or a molded body of the anode material) by an arbitrary method (for example, printing molding) to form a molded body of the solid electrolyte material. And after drying the molded object which provided the material for solid electrolytes, it bakes in an atmospheric condition. The firing temperature at this time is preferably in the range of 1200 ° C. to 1400 ° C., for example, and the firing time is preferably in the range of 1 hour to 5 hours, for example. By this firing treatment, a film-like solid electrolyte 20 is formed on the anode 10, and an anode-solid electrolyte laminate 110 including the anode 10 and the solid electrolyte 20 formed on the anode 10 can be obtained.

<Applying composite material>
Next, as shown in FIG. 2C, the above-mentioned composite material is applied to the surface of the anode-solid electrolyte laminate 110 on the solid electrolyte 20 side. At this time, in order to stably produce a homogeneous electrode, a material prepared by dispersing (or dissolving) a constituent material in one or more dispersion solvents can be preferably used. For example, first, an arbitrary kneading technique (for example, a roll mill, a mixer, etc.) is used for the composite material (powder) disclosed herein, a dispersion solvent (for example, terpineol), and an additive such as a thickener (for example, ethyl cellulose). ), And a method of adjusting to a slurry state can be used. For example, in such a kneading process, the powdery composite material and other additives are kneaded at a stirring speed of 50 rpm to 300 rpm for 0.5 hour to 1 hour, whereby the powdery composite material is suitably dispersed. A slurry-like composite material is obtained.
Then, the slurry-like composite material is applied onto the solid electrolyte 20 by using an arbitrary method (for example, printing molding). In a preferable embodiment of the production method disclosed herein, the application of the composite material may be performed so that the thickness of the cathode formed by the firing is not less than 10 μm and not more than 100 μm. In the manufacturing method disclosed here, since thermal expansion and reductive expansion of the cathode are suppressed, excellent durability can be exhibited even when the electrode is relatively thick.

<Baking of composite materials>
Next, the laminate provided with the composite material is fired. Although the firing method and the like are not particularly limited, for example, the laminate 110 provided with the composite material can be fired at 700 to 900 ° C. (preferably 750 to 850 ° C.). The SOFC 50 in which the cathode 30 is formed by the firing and the anode 10, the solid electrolyte 20, and the cathode 30 are laminated can be obtained.

  Hereinafter, the present invention will be specifically described by way of examples. In this example, 10 types of solid oxide fuel cells (SOFC) having different cathode constituent materials (specifically, the ratio of LSCF and LSTF are different) were produced, and their characteristics and battery performance (power generation performance) were produced. Evaluated. Note that the examples described below are not intended to limit the present invention.

<Production of SOFC>
First, yttria-stabilized zirconia (YSZ) powder having an average particle diameter of 1 μm and nickel oxide (NiO) powder having an average particle diameter of 3 μm were mixed to obtain a mixed powder. The mixed powder, a binder (methacrylic ester polymer), and a dispersant (sorbitan trioleate) were kneaded in a solvent (xylene) to prepare a slurry anode material. The anode material was molded by sheet molding to produce an anode molded body having a diameter of about 20 mm and a thickness of about 1 mm.

  Next, a yttria-stabilized zirconia (YSZ) powder having an average particle diameter of 1 μm, a binder (methacrylic acid ester polymer), and a dispersant (sorbitan trioleate) are kneaded in a solvent (xylene) to form a slurry. A solid electrolyte material was prepared. The solid electrolyte material was printed on the anode molded body to form a solid electrolyte molded body having a diameter of 20 mm. In addition, the thickness of the solid electrolyte molded body at this time was about 20 μm. And after drying the molded object which consists of two laminated | stacked layers, the anode-solid electrolyte laminated body was produced by baking at the temperature of 1300 degreeC for 3 hours.

As the cathode material, a powder of LSCF oxide having an average particle diameter of 0.8 μm (here, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ was used) and an average particle LSTF oxide having a diameter of 0.8 μm (here, La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _3-δ ) was mixed at a mass ratio shown in Table 1 Then, a mixed powder was prepared. The mixed powder was annealed at a temperature of 800 ° C. for 1 hour in an air atmosphere and then pulverized to obtain a powdery composite material (Examples 1 to 10).

<Thermal characteristics evaluation>
The powdery composite material for forming the cathode was subjected to thermomechanical analysis (TMA) under the following conditions, and the thermal expansion coefficient and the reduction expansion coefficient were measured. In the corresponding column of Table 1, the arithmetic average value in the measurement temperature range is shown.
Measuring device: Model “CN8098F1” manufactured by Rigaku Corporation
Measurement method: differential expansion method Measurement temperature range: room temperature (25 ° C.) to 1000 ° C., rate of temperature increase: 5 ° C./min Measurement atmosphere: in the atmosphere of hydrogen 4% + nitrogen 96%

Next, the powdery composite material and a binder (ethyl cellulose) were added to a solvent (terpineol) and kneaded for 0.5 hour with a roll mill to obtain a slurry-like composite material. The slurry-like composite material was screen-molded on the solid electrolyte layer to form a φ16 mm cathode molded body on the solid electrolyte layer. In addition, the thickness of the molded object for cathodes at this time was about 10 micrometers-50 micrometers. And the cathode was formed by baking the molded object which consists of the laminated | stacked 3 layer at the temperature of 800 degreeC for 1 hour.
As a result, anode-supported SOFCs (Examples 1 to 10) in which the anode, the solid electrolyte, and the cathode were laminated in this order were obtained.

<Power generation test>
About the produced SOFC (Examples 1-10), it was made to operate | move at the temperature of 600 to 800 degreeC, and electric power generation characteristic evaluation was performed. As a representative value of “power generation performance”, the value of the maximum power density (W / cm ² ) at a temperature of 700 ° C. is shown in the corresponding column of Table 1. In addition, “-” in the table indicates that fuel gas leaked during the test and measurement was impossible.

As shown in Table 1, as the LSTF content ratio increased, the thermal expansion coefficient and the reduction expansion coefficient gradually decreased. From the viewpoint of thermal expansion, a material having a value close to the thermal expansion coefficient of a typical material used in the SOFC cell disclosed herein is preferable, and the thermal expansion coefficient is 13 to 16 (× 10 ⁻⁶ / K). Example 3 to Example 9 in the range of ^-1 ) were considered suitable. Further, from the viewpoint of the reduction expansion coefficient, Examples 3 to 10 which were relatively small values of 0.7 or less were considered suitable.
Furthermore, although the SOFC disclosed here depends on the application, it is preferable that the maximum power density at a current density of 0.45 A / cm ² is practically 0.1 W / cm ² or more. Therefore, Examples 2 to 8 were considered suitable from the viewpoint of the electrode performance of SOFC.

<Electron microscope observation>
Moreover, the SOFC after the power generation test was disassembled, and the surface of the anode (the surface of the molded body) was observed with a scanning electron microscope (SEM) to confirm the state of the electrode surface. The observation results are shown in FIGS. 3 shows the cathode electrode of Example 1 (that is, only LSCF), FIG. 4 shows the cathode electrode of Example 4 (that is, the content ratio of LSCF and LSTF is 70:30), and FIG. That is, when the content ratio of LSCF and LSTF is 50:50, FIG. 6 corresponds to Example 10 (that is, only LSTF).

The generation of large cracks was observed on the cathode electrode surfaces of Example 1 (FIG. 3) and Example 10 (FIG. 6), which had low power density (or could not be measured) in the power generation test. As a cause, it is conceivable that the thermal expansion coefficient of the material used for constructing the SOFC and the expansion coefficient of the anode molded body were greatly different. Therefore, it is considered that fuel leakage occurred from the crack gap or the resistance increased, leading to deterioration of the power generation performance. On the other hand, in Example 4 (FIG. 4) and Example 6 (FIG. 5), no defects such as large cracks were observed on the electrode surface.
From the above results, by using a cathode material mixed so that the mass ratio of LSCF and LSTF is 80:20 to 30:70, it has excellent electrode performance (high power density), thermal expansion and It was shown that SOFCs with reduced reductive expansion (excellent durability) can be produced.

  According to the material of the present invention, an SOFC cathode having excellent electrode performance and improved durability can be formed. Therefore, the present invention can contribute to the construction of a high-performance SOFC (or power generation system). In addition, when such a material is used, high power generation performance can be exhibited even with a SOFC operating at a low temperature. Furthermore, since the cathode disclosed herein can be directly formed on a solid electrolyte, the operation is simple, and preferably battery characteristics can be improved (for example, resistance can be reduced).

10 Anode (fuel electrode)
20 Solid electrolyte 30 Cathode (Air electrode)
40 Joint 50 SOFC
60 Gas Pipe 110 Anode-Solid Electrolyte Molded Body

Claims (9)

The following general formula (1):
_{(La 1-x Sr x)} (Co y Fe 1-y) O 3-δ (1)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
A perovskite oxide represented by
The following general formula (2):
_{(La 1-x Sr x)} (Ti y Fe 1-y) O 3-δ (2)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
A material for forming a cathode of a solid oxide fuel cell comprising a composite state containing both perovskite type oxides shown in FIG.   The solid oxide form according to claim 1, wherein a mass ratio of the oxide represented by the general formula (1) and the oxide represented by the general formula (2) is 80:20 to 30:70. Cathode forming material for fuel cells.   The material for forming a cathode of a solid oxide fuel cell according to claim 1 or 2, comprising at least one dispersion solvent and prepared in a slurry form. A solid oxide fuel cell comprising an anode, a solid electrolyte and a cathode,
The cathode has the following general formula (1)
_{(La 1-x Sr x)} (Co y Fe 1-y) O 3-δ (1)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
A perovskite oxide represented by
The following general formula (2):
_{(La 1-x Sr x)} (Ti y Fe 1-y) O 3-δ (2)
(Where x is a real number satisfying 0.1 ≦ x ≦ 0.5, y is a real number satisfying 0.1 ≦ y ≦ 0.5, and δ is a value determined to satisfy the charge neutrality condition. is there.)
A solid oxide fuel cell formed in a mixed state with a perovskite oxide represented by   5. The mass ratio of the oxide represented by the general formula (1) and the oxide represented by the general formula (2) in the cathode is 80:20 to 30:70. Solid oxide fuel cell. The cathode, the solid electrolyte, and the anode are formed in a layered manner,
The solid oxide fuel cell according to claim 4 or 5, wherein the thickness of the cathode in the laminated structure is 10 µm or more and 100 µm or less.   The solid oxide fuel cell according to claim 6, wherein the cathode of the laminated structure is formed directly without providing a reaction inhibiting layer on the solid electrolyte. A method for producing a solid oxide fuel cell comprising an anode, a solid electrolyte, and a cathode, comprising:
Providing an anode-solid electrolyte laminate comprising the anode and a solid electrolyte formed on the anode;
Applying the material according to any one of claims 1 to 3 to the surface of the laminate on the solid electrolyte side;
Firing the laminate provided with the material to form the cathode;
A method for producing a solid oxide fuel cell. The manufacturing method according to claim 8, wherein the application of the material is performed so that the thickness of the cathode formed by the baking becomes 10 μm or more and 100 μm or less.